Wash. Rev. Code § 81.53.050
If the commission finds and determines that a change in route of an existing highway, or vacation of a portion thereof, is necessary or advisable, it shall further find and determine what private property or property rights it is necessary to take, damage, or injuriously affect for the purpose of constructing the highway along a new route, and what private property or property rights, will be affected by the proposed vacation of a portion of an existing highway. The property and property rights found necessary to be taken, damaged, or affected shall be described in the findings with reasonable accuracy. In any action brought to acquire the right to take or damage any such property or property rights, the findings of the commission shall be conclusive as to the necessity therefor. A copy of the findings shall be served upon all parties to the cause.
RCW 81.53.050